Using Ca2+-selective microelectrodes, the effects of 3,4-diaminopyridine (DAP) on myoplasmic calcium ([Ca2+](i)) were studied in frog sartorius muscle fibers. DAP induced an increase of [Ca2+](i) in a concentration-dependent manner. DAP 1 mmol · L-1 increased the [Ca2+](i) from control 166 ± 41 nmol · L-1 to 416 ± 69 nmol · L-1 (n = 10). In the absence of external calcium, DAP still enhanced [Ca2+](i). [Ca2+](i) of the fibers bathed in Ca2+-free Ringer's solution containing DAP 1 mmol · L-1 was 152 ± 43 nmol · L-1, which was significantly higher than 77 ± 35 nmol · L-1 of [Ca2+](i) of the fibers in Ca2+-free Ringer's solution. In addition, DAP promoted the hydrolysis of phosphoinositides, and DAP induced hydrolysis was more in the presence of external calcium. It is suggested that, through enhancing the hydrolysis of phosphoinositides, DAP released Ca2+ from intracellular Ca2+ store in frog sartorius muscle fibers.
|Original language||English (US)|
|Number of pages||3|
|Journal||Acta Pharmacologica Sinica|
|State||Published - Jan 1 1994|
ASJC Scopus subject areas